Oil pump and oil system for air compressor



March 22, 1965 A. 1. MIHALAKIS OIL PUMP AND OIL SYSTEM FOR AIR COMPRESSOR 2 Sheets-Sheet 1 Filed July 15, 1964 March 22, 1966 A. i. MlHALAKls OIL PUMP AND OIL SYSTEM FOR AIR COMPRESSOR 2 Sheets-Sheet 2 Filed July 15. 1964 W .nvxwhi WWW.

hv: .AUNNNi m llll United States Patent Office 3,241,747 Patented Mar. 22, 1966 3,241,747 GIL PUMP AND OIL SYSTEM FDR A111 COMPRESSUR Agis I. Mihalakis, Northridge, Calif., assignor to George V. OHaver, Canoga Park, Calif. Filed `Iuly 15, 1964, Ser. No. 382,833 10 Claims. (Cl. 2311-207) This invention relates to an improved oil pump and to 'au oil system for a rotary air compressor of the vane type. Such a compressor is shown in my prior patent, No. 3,107,846. It is highly desirable to circulate oil through the working parts of the compressor for purposes of lubrication as well as to prevent overheating of the parts. Accordingly, it is an important object of this invention to provide an improved oil pump which may be used for this purpose, which has relatively few operating parts, is rugged in character, relatively inexpensive to manufacture, Ireadily capable of producing oil pressures up to 250 p.s.i., and is particularly adapted for use between the rotating shaft and stationary housing of a machine.

Another object is to provide such an oil pump assembly which permits endwise movement of the shaft.

A more detailed object is to provide an improved oil pump having a pair of duplicate vanes mounted to reciprocate radially in a transverse slot in the shaft and cooperating with a stationary eccentric cavity positioned within an enclosing ring or body member.

Another object is to provide a device of this type in which the reciprocating vanes are each provided with a longitudinal opening and a lateral port which acts as a valve to utilize the pressure of the oil being pumped to assist in maintaining the spring-urged vane in sliding contact with the cylind-rical surface of the offset cavity.

Another object is to provide a pump assembly of this type in which each of the vanes is provided with a projecting lip which travels in a groove on the stationary enclosing member, to prevent canting or tilting of the vanes.

Another object is to provide an oil pump assembly of this type in which the portion of the groove which is in communication with both the inlet and discharge ports serves as a bypass which is used to unload pressure in the oil system whenever rotation of the shaft ceases.

Other and more detailed objects and advantages will appear hereinafter.

In the drawings:

FIGURE 1 is a schematic view showing an oil pumping and filtering system as applied to an air compressor.

FIGURE 2 is a sectional elevation taken substantially on the lines 2 2 as shown in FIGURE 1 and showing details of the oil pump.

FIGURE 3 is a transverse sectional elevation partly broken away and taken substantially on the lines 3-3 as shown in FIGURE 2.

FIGURE 4 is a transverse sectional elevation partly broken away and taken substantially on the lines 4-4 as shown in FIGURE 2.

FIGURE 5 is a sectional detail taken substantially on the lines 5 5 as shown in FIGURE 4, the shaft and associated parts being turned one quarter revolution.

FIGURE 6 is a fragmentary sectional view taken substantially on lines 6 6 as shown on FIGURE 4.

FIGURE 7 is a perspective View of one of the radially reciprocal vanes.

Referring to the drawings, the air compressor generally designated 10 includes a stationary housing 11 and a rotary shaft 12. Air is drawn into the compressor through the inlet pipe 13 and air-inlet lter 14. Compressed air with entrained oil is discharged from the compressor 10 through outlet pipe 15 to the oil separator assembly generally designated 16. Entrained oil is separated from the air and carried through a pipe 17 to the oil cooler and reservoir 18. The clean air with the oil removed passes from the separator assembly 16 through the check valve 19 and to a receiver, not shown, through delivery pipe 20.

In order to provide a supply of oil under .pressure for lubricating the internal parts of the air compressor 10 as well as for removal of heat, an oil pump assembly generally designated 25 is mounted on the housing 11 and driven by the rotary shaft 12. The oil pump assembly 25 includes a ring or body 26 mounted within a bore 27 on one of the parts of the housing 11. The ring 26 has an eccentric bore surface 28 encircling a portion of the drive shaft 12. The bore surface 28 is cylindrical but is offset laterally from the axis of the shaft 12 and is larger than the cylindrical portion of the shaft 29, which it encircles. The bore 28 has only running clearance with the surface 29 of the shaft at one tangent location, designated 30, and has maximum spacing from the shaft at a diametrically opposite position, so that a crescent-shaped space 31 is defined between the outer surface 29 of the shaft 12 and the bore 28 in the ring 26.

A slot 32 extends transversely through the shaft 12, and the side walls 33 of the slot are parallel to the shaft axis. Radially movable vanes 34 and 35, which are duplicates, are mounted in sliding contact with the side walls 33. The end walls 36 of the slot 32 are spaced apart by a distance greater than the axial thickness of the vanes 34 and 35 to provide clearance space to permit axial movement of the shaft 12 in either direction relative to the housing 11 and stationary ring or body 26. Each of the vanes 34 and 35 is provided with parallel surfaces 37 in sliding contact with the side walls 33. Each of the vanes 34 and 35 has a convex, arcuate surface 38 at its projecting end, and this surface 38 has sliding contact with the surface of the bore 28 in the body 26. As the shaft 12 turns, the vanes 34 and 35 reciprocate radially within the transverse slot 32.

The side face 40 of the body 26 is provided with a groove 41 which is concentric with the bore 28. Each of the vanes 34 and 35 has a lip 42 which projects beyond the arcuate surface 38 and which has an arcuate surface 43 concentric with the arcuate surface 38. The lips 42 on the vanes 34 and 35 each project into the groove 41, and the arcuate surfaces 43 on the vanes have close running clearance with the cylindrical bore surface 44 of the groove 41.

Each of the vanes 34 and 35 is provided with a central opening 46 extending longitudinally of the vane. The opening is open at the inner end of each vane, but does not project into the arcuate surfaces 38 or 43. A coil compression spring 47 extends into each of the openings 46 and rests against the bottom of each opening. The action of the spring 47 is to apply a force tending to move the vanes 34 and 3S in opposite radial direction and to maintain Contact of the arcuate surfaces 38 With the surface of the internal bore 28. As the shaft turns from the position shown in FIGURE 4 to the position shown in FIGURE 5, the space between the adjacent ends of the vanes 34 and 35 increases from a minimum to a maximum.

Means are provided for supplementing the action of the spring 47 Iby utilizing the pressure of the fluid being pumped, and, as shown in the drawings, this means a lateral port 48 provided on the leading surface 37 of each Vane 34 and 35. This port 48 is positioned so that it is exposed to the crescent-shaped space 31 for slightly more than one-half of a revolution of the shaft 12 and disappears into the slot 32 when the particular vane approaches the tangent region 30. Thus, as shown in FIG- URE 4, the port 48 on the vane 34 is almost closed in the position of the part as shown. As the shaft 12 continues to rotate in the direction of the arrow 49, the vane 34 moves radially inward, closing ofr the port 48. The port does not reopen until the vane 34 has rotated nearly one-half revolution, at which time the radial movement of the vane in an outward direction re-exposes the port 48 to the crescent-shaped space 31. The exposure of the port 48 to the pressure applied to the leading face of the vane transmits the pressure into the interior openings 46 of both vanes 34 and 35 and acts to overcome the ffuid pressure acting on the extreme outer end of the vane at the arcuate surface 38 and also against the lip surface 43.

The purpose of the projecting lips 42 on the vanes 34 and 35 is to prevent possible canting or tilting of the outer ends of the vanes to a degree permitting interference between the vane and the internal cylindrical surfaces 50 and 51 on the stationary parts 52 and 53, respectively, on opposite sides of the body 26. While the surfaces 39 of the vanes 34 and 35 have considerable clearance with respect to the end walls 36 of the transverse slot 32, they have sliding tits with respect to the stationary side walls 54 and 55 of the parts 52 and 53. The clearance -between the vanes 34 and 35 and the end walls 36 of the transverse slot 32 is essential in order to accommodate axial movement of the shaft 12 with respect to the housing 11 and body 26. Such axial movement may result from differential thermal expansion. Furthermore, some clearance space in the axial direction is necessary for manufacturing and assembly tolerances to prevent the shaft from applying side loads to the reciprocating vanes.

The Ibody 26 is provided with a lateral discharge port 55 and a lateral inlet port 56. These ports extend axially through the body 26. As shown in FIGURE 3, the discharge port 55 is connected to the crescent-shaped cavity 31 by means of the ilow channel 56 extending into the side face 57 of the body 26. A similar ow channel 58 extending into the same side face 57 connects the inlet port 52 with the crescent-shaped space 31. These ow channels are separated by the bridge 60 which constitutes that portion of the 'body 26 which has the close running clearance 30 with the shaft 12. The face 40 of the body 26 is also provided with flow channels 61 and 62 as shown in FIGURE 4, connecting the discharge port 54 and the inlet port 55, respectively, to the groove 41. That portion of the groove 41 which traverses the :bridge 60 is designated 41a, and this serves 'as a bypass between the ports 54 and 55, except when one of the lips 42 passes through it. This bypass has certain important advantages as described below.

As shown in FIGURE 6, the discharge port 54 in the ring or body 26 communicates via passage 65 in the coverplate 53 with the terminal fitting 66. This terminal fitting communicates with discharge line 17 as shown in FIGURE 1. Similarly, inlet port 55 in the ring or body 26 communicates by way of passageway 67 with a terminal fitting for connection with the inlet pipe 68 shown in FIGURE 1 and leading from the oil cooler and reservoir 18. The coverplate 53, ring or body 26, and spacer ring 52 are clamped in position against the housing 11 by means of threaded fastenings 70. The spacer ring 52 contacts the outer race of a bearing assembly 71, but is relieved to avoid contact with the inner race of the bearing assembly. The bearing assembly 71 is one of a pair rotatably supporting the shaft 12 within the housing 11. A locating pin 72 is positioned within aligned apertures formed in the coverplate 53 and the body 26 so that the inlet and discharge passages 67 and 65 in the coverplate 53 register with the ports 55 and 54, respectively, in the body 26. A conventional oil seal assembly 75 is provided in the coverplate 53 to prevent oil leakage along the shaft. An O-ring 76 is compressed in a peripheral groove to prevent leakage between the coverplate 53 and the body 26.

In the operation of the pump assembly 25, oil is supplied to the inlet port 55 through pipe 68, and oil is discharged from discharge port 54 through pipe 17. When the shaft 12 is rotated by means not shown, the vanes 34 and 35 are caused to reciprocate radially `within the transverse slot 32 as their convex-curved ends 38 slide within the cylindrical offset bore 28. Considering FIG- URE 3, oil in the crescent-shaped space 31 in advance of the vane 35 and behind the vane 34 is delivered through channel 56 to the discharge port 54, while oil from the inlet port 55 passes through channel 58 into the space behind the vane 35. The coil spring 47 within the vanes 34 and 35, supplemented by internal oil pressure admitted through ports 48, holds the outer curved ends 38 of the vanes in contact with the internal cylindrical bore 28.

While the vanes 34 and 35 each have a sliding fit between the parallel side walls 33 of the transverse slot 32, they have axial clearance between the end walls 36, and hence would be free to cant or to tilt to some extent. Such a tilting or canting movement is prevented by the sliding engagement of the projecting tips 42 on each of the vanes 34 and 35, traveling in the continuous groove 41. A discharge of oil from the groove 41 occurs through channel 61 to the discharge port 54, and oil from the inlet port 55 enters the groove 41 by way of the channel 62.

When the compressor shaft 12 is rotating, the oil discharged through pipe 17 passes through check valve 80 and then passes through lines 82 and 83 back to the interior of the air compressor to lubricate the parts thereof, and to remove heat. Oil in the line 82 passes through another check valve 84 before reaching the interior of the compressor. The oil is discharged from the compressor along with the compressed air to discharge pipe 15. The compressed air with entrained oil enters the first charnber 85 of the separator 16. A major portion of the oil is separated from the air in the rst chamber 8S and 'passes outward under pressure through the discharge pipe 86. The air with small quantities of entrained oil then passes around the external bypass 87 into the second chamber `88. The chambers are separated by the divider plate 89. If desired, the external bypass 87 may be eliminated and an opening in the upper portion of the divider plate 89 substituted therefor. Both chambers may contain felt pads or other suitable material for separating the entrained oil from the stream of compressed air. Oil from the second chamber 88 passes outward through check valve 90 and line 91. The lines 86 and 91 both communicate with the return line 17, which carries the oil back to the cooler and reservoir 18.

The device 18 which takes the form of the heat exchanger or radiator does not operate under pressure. The upper chamber 92 and lower chamber 93 are connected by a plurality of vertical tubes 94, each having fins 95 for ecient heat exchange. An oil ll and dipstick assembly 96 is provided in the upper chamber 92, and a drain 97 is provided within the lower chamber 93. A vent line 98 connects the upper chamber 92 of the reservoir 18 to the air-inlet pipe 13, so that oil fumes are returned to the compressor.

A pressure line 101 is connected by terminal tting 102 to passages 104, 105, and 106, which communicates with the uppermost portion of the crescent-shaped chamber 31. The passage 106 intersects the cylindrical bore surface 28. The pressure line 101 communicates with the pilot-operated shutoff valve 110 which acts to close an unloading line 1111, leading from the second chamber 88 of the oil separator 16. A bleed valve 112 is provided in the pressure line 101, and a pressure gauge 113 is also connected to the pressure line 101. The bleed valve 112 is opened under initial start-up conditions, only, and remains closed until such time as the oil is changed or the pump parts are disassembled.

Whenever the shaft 12 rotates, the pump assembly 25 delivers pressure through the line 101 to close the valve 110 and prevent fiow through the unloading line 111. When the compressor is shut off, however, and the shaft -12 stops rotating, the pressure in the crescent-shaped cavity 31 falls very rapidly, as pointed out below, and the valve 110 opens the unloading line 111 to atmosphere through a muiiier. This vents the crescent-shaped space 311 to atmosphere, so that no pressure is available to force any additional oil into the inte-rior of the compressor. This is important to prevent hydraulic lookup when the compressor is again started.

Pressure is quickly bypassed Within the pump assembly 2-5 from the discharge port 5'4 to the inlet port 55, when the shaft 12 stops rotating, and this bypass occurs through the groove portion 41a and also through the groove 114 at the bridge 60, as shown in FIGURES 3 and 5. The size of the groove 114 also affords a means of determining the capacity of the pump assembly the larger the groove 114, the greater the bypass capacity between theinlet and discharge ports, and theA lower the pump capacity.

Having fully described my invention, it is to be understood that I am not to Ibe limited to the details herein set forth, but that my invention is of the full scope of the appended claims.

I claim:

1. In a rotary pum the combination of: a rotary shaft having an outer cylindrical surface interseoted by a central transverse slot, a stationary body having a bore encircling a port-ion of the shaft, said bore being defined by an internal cylindrical surface laterally offset with respect to said shaft surface, the body having a groove concentric with and intersecting said bore surface, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact wtih said bore surface, the lip of each vane being received in said groove, the body having an inlet port and a discharge port, and the body having passage means on opposite sides of said tangent portion communicating with said bore and with each of said ports, respectively.

2. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by a central transverse slot, said slot being formed by axially spaced end walls and by laterally spaced side walls, the side walls being parallel to the axis of the shaft, a stationary body having a bore encircling a portion of the shaft, said bore Vbeing defined by an internal cylindrical surface of larger diameter than said shaft surface, a portion of said bore surface being tangent to said shaft surface, t-he body having a groove concentric with and intersecting said bore surface, a pair of duplicate vanes mounted in said slot in sliding contact with said side walls and having axial clearance with respect to said end walls, the vanes being mounted to reciprocate radially in said slot, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a coil compression spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, the body having an Iinlet port and a discharge port, and the body having passage means on opposite sides of said tangent portion communicating wit-h said bore and with the inlet port and discharge port, respectively.

3. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by ya central transverse slot, said slot being formed by axially spaced end walls and by laterally spaced side walls,

the side walls being parallel to the axis of the shaft, a stationary body having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface of larger diameter than said shaft surface, a portion of said bore surface being tangent to said shaft surface, the body having a side face provided with a groove concentric with and intersecting said bore surface, a pair of duplicate vanes mounted in said slot in sliding contact with said side walls and having axial clearance with respect to said end walls, the vanes being mounted to reciprocate radially in said slot, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a coil compression spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, the body having an inlet port and a discharge port, and flow channels formed in the side face of the body, one of the flow channels connecting the discharge port to said bore on one side of said tangent portion, and the other flow channel connecting the inlet port to said bore on the other side of said tangent portion.

4. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by a central transverse slot, a stationary body having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface laterally offset with respect to said shaft surface, the body having parallel side faces, one of said side faces being provided with a groove concentric with and intersecting said bore surface, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, the body having an inlet port and a discharge port, the body having passage means on opposite sides of said tangent portion communicating with said bore and said ports, respectively, and communicating with said groove and said ports, respectively.

5. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface .intersected by a central transverse slot, a stationary body -having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface laterally offset with respect to said shaft surface, the body having parallel side faces, one of said side faces being provided with a groove concentric with and intersecting said bore surface, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, the body having an inlet port and a discharge port, and flow channels formed in the side faces of the body on opposite sides of said tangent portion communicating with said inlet port and discharge port, respectively, the flow channels on one side face communicating wit-l1 the internal bore and the iiow channels on the other side face communicating with said groove.

6. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by a cent-ral transverse slot, a stationary body having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface laterally offset with respect to said shaft surface, the body having a groove concentric with and intersecting said bore surface, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, each vane having a central longitudinal opening and a lateral port near said convex-curved surface communicating with said opening, the body having an inlet port and a discharge port, and the body having passage means on opposite sides of said tangent portion communicating with said bore and with each of said ports, respectively.

7. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by a central transverse slot, said slot being formed by axially spaced end walls and by laterally spaced yside walls, the Side walls being parallel to the axis of the shaft, a stationary body having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface of larger diameter than said shaft surface, a portion of said bore surface being tangent to said shaft surface, the body having a groove concentric with and intersecting said bore surface, a pair of duplicate vanes mounted in said slot in sliding contact with said side walls and having axial clearance with respect to said end walls, the vanes being mounted to reciprocate radially in said slot, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a coil compression spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said bore surface, the lip of each vane being received in said groove, each vane having a central longitudinal opening and a lateral port near said convex-curved surface communicating with said opening, the body having an inlet port and a discharge port, and the body having passage means on opposite sides of said tangent portion communicating with said bore and with the inlet port and discharge port, respectively.

8. In a rotary pump, the combination of: a rotary shaft having an outer cylindrical surface intersected by a central transverse slot, said slot being formed by axially spaced end walls and by laterally spaced side walls, the side walls being parallel to the axis of the shaft, a stationary body having a bore encircling a portion of the shaft, said bore being defined by an internal cylindrical surface of larger diameter than said shaft surface, a portion of said bore surface being tangent to said shaft surface,the body having a groove concentric with and intersecting said bore surface, a pair of duplicate vanes mounted in said slot, said vanes each having side surfaces in sliding contact with said side walls and having axial clearance with respect to said end walls, the vanes being mounted to reciprocate radially in said slot, each vane having an end portion provided with a convex-curved surface and a radially projecting lip, a spring interposed between said vanes acting to maintain their respective convex-curved surfaces in sliding contact with said groove, each vane having a central longitudinal opening and a lateral port in its side surface communicating with said opening, the body having an inlet port and a discharge port, and the body having passage means on opposite sides of said tangent portion communicating with said bore and with the inlet port and discharge port, respectively.

9. In an oil system for an air compressor having a rotary shaft, a housing and an air discharge pipe connected to the housing, the combination of: walls on a cylindrical portion of the shaft defining a central transverse slot in the shaft, a stationary body fixed relative to the housing and having an offset cylindrical bore tangent to the cylindrical portion of the shaft to define a crescentshaped chamber, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion, means acting on said vanes t0 maintain their respective end portions in sliding contact with said bore surface, the body having an oil inlet port and an oil outlet port, the body having passage means on opposite sides of said tangent portion communicating with said bore and each of said ports, respectively, means for delivering oil from said discharge port to the interior of the compressor, a pressure unloader line operatively connected to the air discharge pipe, a pressure-operated valve for closing said unloader line, conduit means for connecting said crescent-shaped chamber to said valve for closing said unloader line when the crescent-shaped chamber is pressurized by action of said vanes when the shaft is rotated, and for opening the unloader line when said chamber is vented, and bypass means adjacent said tangent portion connecting said inlet and discharge ports for venting said chamber.

10. In an oil system for an air compressor having a rotary shaft, a housing and an air discharge pipe connected to the housing, the combination of: walls on a cylindrical portion of the shaft defining a central transverse slot in the shaft, a stationary body fixed relative to the housing and having an offset cylindrical bore tangent to the cylindrical portion of the shaft to define a crescentshaped chamber, a pair of duplicate vanes slidably mounted in said slot to reciprocate radially, each vane having an end portion, means acting on said vanes to maintain their respective end portions in sliding contact with said bore surface, the body having an oil inlet port and an oil outlet port, the body having passage means on opposite sides of said tangent portion communicating with said bore and each of said ports, respectively, means for delivering oil from said discharge port to the interior of the compressor, an oil separator connected to the air discharge pipe of the compressor, a pressure unloader line connected to the oil separator, a pressure-operated valve for closing said unloader line, conduit means for connecting said crescent-shaped chamber to said valve for closing said unloader line when the crescent-shaped chamber is pressurized by action of said vanes when the shaft is rotated, and for opening the unloader line when said chamber is vented, and bypass means adjacent said tangent portion connecting said inlet and discharge ports for venting said chamber.

References Cited by the Examiner UNITED STATES PATENTS ROBERT M. WALKER, Primary Examiner. 

1. IN A ROTARY PUMP, THE COMBINATION OF: A ROTARY SHAFT HAVING AN OUTER CYLINDRICAL SURFACE INTERSECTED BY A CENTRAL TRANSVERSE SLOT, A STATIONARY BODY HAVING A BORE ENCIRCLING A PORTION OF THE SHAFT, SAID BORE BEING DEFINED BY AN INTERNAL CYLINDRICAL SURFACE LATERALLY OFFSET WITH RESPECT TO SAID SHAFT SURFACE, THE BODY HAVING A GROOVE CONCENTRIC WITH SAID INTERSECTING SAID BORE SURFACE, A PAIR OF DUPLICATE VANES SLIDABLY MOUNTED IN SAID SLOT TO RECIPROCATE RADIALLY, EACH VANE HAVING AN END PORTION PROVIDED WITH A CONVEX-CURVED SURFACE AND A RADIALLY PROJECTING LIP, A SPRING INTERPOSED BETWEEN SAID VANES ACTING TO MAINTAIN THEIR RESPECTIVE CONVEX-CURVED SURFACES IN SLIDING CONTACT WITH SAID BORE SURFACE, THE LIP OF EACH VANE BEING RECEIVED IN SAID GROOVE, THE BODY HAVING AN INLET PORT AND A DISCHARGE PORT, AND THE BODY HAVING PASSAGE MEANS ON OPPOSITE SIDES OF SAID TANGENT PORTION COMMUNICATING WITH SAID BORE AND WITH EACH OF SAID PORTS, RESPECTIVELY. 